This invention relates to ball nut assemblies, and, more particularly, this invention relates to a ball return liner within a ball nut that allows for slight adjustment within the ball nut.
Ball screw assemblies may be used to translate rotary motion to linear motion and linear motion to rotary motion. Most ball screw assemblies include an elongate ball screw, and a ball nut body. The ball nut body in cooperation with the ball screw direct a plurality of ball bearings through an internal bearing race formed between the ball nut body and ball screw upon rotation of the ball screw. The ball bearings translate rotary motion of the ball screw to linear motion of the ball nut body. Both the elongate ball screw and ball nut body commonly include a continuous helical groove which defines the internal bearing race.
The traditional ball nut return designs are featured in either fixed pockets or returned tubes without floating ability. For manufacturing such ball nut returns, substantial operations arc required to produce the precise pockets or holes prior to and after heat treatment. Thus, manufacturing costs are high and work-in-process (xe2x80x9cWIPxe2x80x9d) is significant, and the consistency of the quality is a continual concern.
Due to the very tight envelope nature design of the rack and ball nut assembly, there exists stringent requirements for the electric power steer (xe2x80x9cEPSxe2x80x9d) product lash movement. The movement requires as little as .0125 mm in axial directions, which promotes a tremendous technical aspect for manufacturability during the high volume production. The match of rack thread form versus ball nut thread is becoming an unavoidable necessity and brings many more complications. In addition, more precise tolerances and expensive operations would be expected.
One example of a ball nut with ball return uses a deflector segment having rectangularly shaped corners which must be received in a longitudinal slot in a ball nut body. From a manufacturing perspective, care must be taken to ensure that the S-shaped return grooves in the deflector segment match up with the plurality of arcuate grooves within a sleeve segment when assembled since the cooperating deflector segment is fixed within the longitudinal slot. Misalignment of the arcuate grooves with the S-shaped return grooves in the deflector segment is compensated by utilizing a smaller ball bearing diameter, which may lead to a smaller load capacity limitation and shorter product life potential.
The manufacturing of ball nut return slots for a ball nut and return system can include a number of operations including heat treatment, xe2x80x9cjig grindingxe2x80x9d, polishing and size inspection for part matching, however the highest cost driver of operations is jig grinding. The operation has been adapted either in the tool room or aerospace industries for limited production and selective operation. This is due to the nature of a slow machine cycle time and expensive capital investment.
The fixed pocket and hole return product design thus offers sophisticated manufacturing challenges in terms of the manufacturing cost, machining cycle time, quality consistency, component matching and WIP issues. In short, the current and traditional design is not cost effective and would not provide any significant competitive advantages that would penetrate the EPS market.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a ball nut and return liner assembly including a ball nut having a tubular body having a longitudinal axis, the tubular body having an inner surface and an outer surface, a plurality of arcuate grooves defined on the inner surface. A longitudinal slot is defined on the inner surface parallel to the longitudinal axis, interrupting the plurality of arcuate grooves, and forming a pocket for receiving the return liner, the longitudinal slot having first curved walls. The return liner is provided with a first surface having a plurality of S-shaped return grooves extending from the first side to the second side to cooperate with the plurality of arcuate grooves in the ball nut. The return liner is further provided with a second surface for fitting within the longitudinal slot within the ball nut, the second surface having second curved walls.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.